1. Technical Field:
The present invention relates to a resin cleaning system. Particularly, it relates to a system for cleaning ion exchange resins in water treatment plants.
2. Description of the Related Art:
The cleaning of ion exchange resins has been practiced for many years to improve the performance of fouled resin and lengthen its useful life. In water plants, in particular, a resin bed comprised of ion exchange beads is commonly used to remove impurities from water by passing the processed water over and through an ion exchange resin bed in order to remove contaminants.
The ion exchange bead can be compared in many ways to a sponge. A single resin bead that is removed from the bed, while appearing dry, actually may contain approximately 50%. water by weight. In addition, while the bead appears to be rigid and hard to the touch, it is actually very flexible and permeable to the water that passes through the resin bed. In fact, the water volume present in a resin bead at any time may vary by more than 30% in common water treatment applications. This change in water volume is driven by the flux created by the difference in concentration of ions in the solution surrounding the bead and the type of ion that is loaded on to the resin's active sites by the solution. As a result, the resin beads can respond almost like a sponge in that they can be "squeezed", i.e., they can have solution flushed from the surface and interior of the bead through varying ion concentration, concentration of cleaning chemicals, and temperature.
The majority of water treatment plants do not have a separate vessel for cleaning so that this cleaning occurs in the service vessel. In addition, current cleaning methods rely on the use of cleaning chemicals that act as a solvent to clean the beads. For example, one presently used method for removing organics from anion exchange resins employs strong base anion and weak anion resin types. Organics are removed by backwashing the resin bed at the regular flow rate and then draining to bed level. Then, the resin is air lanced for thirty minutes at four cubic feet of air per minute, per cubic foot of resin, backwashed at a regular flow rate for twenty minutes, and then drained to bed level. Next, 10 gallons brine and caustic solution is added at 140.degree. F. per cubic foot of resin. The brine and caustic solution is allowed to soak for two to three hours. Thereafter, the resin is rinsed with a down flow of two gallons per minute, per cubic foot of resin with clean water for fifteen minutes, and the treatment is repeated if necessary. Afterwards, the resin bed is backwashed at the regular flow rate for ten minutes. Then the resin is rinsed and regenerated, and the unit is returned to service.
While several conventional methods have agitation, such as air agitation, this type of agitation provides very little physical movement of the resin when compared to the hydraulic jet used in the bead jet. Air lancing is also labor intensive and may damage the service vessel internals. Greater agitation that might be provided by a centrifical pump or propelled type mixer is known to damage the ion exchange resin. While conventional methods may recirculate the cleaning chemicals through the ion exchange resin, there are no current methods that take advantage of the repeated squeezing phenomena that can be imposed on the resin beads without using large amounts of cleaning chemicals in repeated conventional cleanings.
Currently, the prior art does not provide a system that efficiently provides physical cleaning of the resin without scratching or otherwise damaging the ion exchange resin.